HighResolution Numerical Analysis of the Triggeri

Authors: Huihong Cheng Huai Zhang Yaolin Shi

Publish Date: 2015/11/05

Volume: 173, Issue: 5, Pages: 1593-1605

PDF Link

Abstract

In 1981 a powerful M L57 earthquake occurred 50 km away from the Aswan Reservoir dam After the statistical analysis on the correlationship between longterm continuous seismicity occurrence and the reservoir water level variation attributed to the impoundment and drainage procedures researchers believe that this event is a typical reservoirtriggered seismicity Nature 301614 1983 Earthquake Activity in the Aswan Region Egypt Birkhäuser Basel pp 69–86 1995 although its triggering mechanism is poorly understood to date To quantitatively address the triggering mechanism as well as its relationship with the characteristics of local geological settings around the reservoir region in this paper a fully coupled threedimensional poroelastic finite element model of the Aswan reservoir is put forward by taking the consideration of the realistic observation data for example the highresolution topography water level fluctuation history flood zone boundary and water depth variation fault parameters etc Meanwhile the change of Coulomb Failure Stress ΔCFS in correspondence to elastic stress and pore pressure variations induced by fluid diffusion is calculated And the elastic strain energy accumulation in the reservoir region due to the impoundment load is obtained as well Our primary results indicate that both the pore pressure and the coulomb stress on the seismogenic fault plane gradually increase with the respect of time while the water level rises The magnitude of ΔCFS at the hypocenter of this major event is around 01 MPa suggesting that the impoundment of the Aswan Reservoir possibly triggered the M L57 earthquake The contribution of the elastic load is less than 3 percent of the total ΔCFS on the other hand the dynamic pore pressure change predominantly accounts for the contribution The accumulative maximum surface deformation beneath the Aswan reservoir is up to 80 cm since its impounding began until the M L57 earthquake occurred Although the total elastic strain energy accumulation caused by the impoundment water load is around 10 × 1010J this energy density still insignificant compared to that of the vast reservoir inundation area as it is only less than few percent of the total energy released by the major event which confirms that the sustained regional geological loading controls the occurrence of this large reservoirinduced event Furthermore elastic loading and pore fluid pore pressure diffusion due to the impoundment of the Aswan reservoir might accelerate its occurrenceThis research work is supported National Basic Research Program of China under grant number 2014CB845906 and R and D of Key Instruments and Technologies for Deep Resources Prospecting the National RD Projects for Key Scientific Instruments under grant number ZDYZ201210204 It is also partially supported by the CAS/CAFEA international partnership Program for creative research teams No KZZDEWTZ19 and KZZDEWTZ15

Keywords: